In developing countries many millions of people fall victim to waterborne diseases each year. Yearly about 250 million new cases of waterborne infections are reported world-wide, resulting in 1.8 million fatalities ensuing from diarrhoeal diseases, of which 90% are children under the age of 5. In India alone, yearly 320 thousand children die from diarrhoea. Almost invariably this is due to a lack of reliable and cost-effective water production technology, sanitation and hygiene, resulting in unsafe water or water of poor bacteriological quality. Moreover, there is a lack of systems for assessing the bacteriological quality of water. Use of safe drinking water can reduce diarrhoeal morbidity by between 6 to 25%. If water is unsafe, it can be treated. In fact, chlorination at point of use can decrease diarrhoea by 35 to 39%. Therefore, there is a need for systems for assessing the bacteriological quality of water at the point of use, to determine whether treatment is necessary.
The most common cause of waterborne disease is faecal contamination. Most often, drinking water is contaminated with animal and human excrement. Faecal contamination of drinking water is usually not noticed due to lack of affordable diagnostic methods. In order to detect faecal contamination use can be made of so-called indicator organisms. An indicator organism to detect faecal contamination: i) is universally present in large numbers in the faeces of humans and warm-blooded animals; ii) readily detected by simple methods; iii) exhibits no growth in natural waters; and iv) persists in water and can be removed by water treatment similar to waterborne pathogens. A very suitable faecal indicator organism, and the one designated by the World Health Organization (WHO) for that purpose, is Escherichia coli. More precisely, an indication of faecal contamination can be obtained by the determination of the number per 100 ml of water of coliforms (facultatively-anaerobic, rod-shaped, Gram-negative, non-sporulating bacteria that ferment lactose; including for instance species of the genera Escherichia, Enterobacter, Kebsiella and Citrobacter) and especially the thermotolerant coliform Escherichia coli. 
With respect to the test system for detecting Escherichia coli, the WHO has introduced the acronym ASSURED to describe the ideal properties and criteria of a diagnostic test which stands for: Affordable (for those at risk of infection); Sensitive (few false negatives); Specific (few false positives); User-friendly (simple to perform and requiring minimal training); Rapid (to enable treatment at first visit) and robust (does not require refrigerated storage); Equipment-free; and Deliverable to developing countries. Numerous methods have been used for the detection of coliforms and E. coli in water. These detection methods can be based on for instance cultivation, enzyme reaction, and immunological or genetic detection. Currently there are more than 30 alternative assays commercially available to detect coliforms and E. coli. Most of these tests do not comply with the ASSURED criteria for speed and sensitivity, or for not being equipment free. In fact, most require a dedicated laboratory in order to meet the most essential test criteria for being sensitive and specific. It should be understood, however, that a rapid field test for faecal contamination that is less sensitive than the laboratory tests may result in a significant reduction of sick people and save lives. Thus, a sensitive laboratory test is not always more useful than a less-sensitive, but rapid and specific field test that does the job, i.e. that tells the user that the water is unsafe to drink.
Thus, there is a need for a simple, cheap, robust and fast test method for on site detection of faecal contamination in water. Such a method will be used more frequently, at more places by more people and can warn people earlier, and as a consequence, save lives.